1. Technical Field
The present invention relates to a projection optical system suitable for being incorporated into a projector that enlarges and projects an image of an image display element, and a projection-type image display device incorporating the projection optical system.
2. Related Art
In recent years, as projectors have higher luminance and higher resolution, a heat load increases on the optical path of projection light, and therefore, some projectors use a light shielding plate (diaphragm) in a projection optical system in order to, for example, deal with defocusing (e.g., refer to JP-A-2012-189837). A projection lens disclosed in JP-A-2012-189837 includes a plurality of lens groups, in which a metal diaphragm satisfying prescribed conditions such as reflectance is disposed on the exiting side of the lens group that is close to the illumination system side and on the incident side of the lens group that is next to the above-mentioned lens group and located on the screen side.
In the projection lens disclosed in JP-A-2012-189837, however, stray light impinges on an exiting-side lens frame of the group on the screen side, so that the temperature rise is expected in that portion, and in addition, the impinging of the stray light on the frame causes an increase in flare. As the projector has higher luminance, there is the possibility that the temperature of the lens frame portion may exceed the heat-resistant temperature of plastic.